A Labrador-Sized Scorpion Once Roamed Britain

A metre-long scorpion with 16-centimetre pincers once hunted the floodplains of what is now England and Wales. It was doing this 415 million years ago, before trees existed, and it was very likely hunting fish.

The fossils of Praearcturus gigas have been sitting in the Natural History Museum in London since the 19th century. When the species was first described in 1871, British scientist Henry Woodward classified it as a giant woodlouse-like crustacean. The error was so foundational it shaped the fossil's scientific name: "Arcturus" refers to a group of marine isopods, not arachnids. The specimen spent 155 years in the wrong drawer.

A new study published in the journal Palaeontology has now reclassified Praearcturus as one of the largest scorpions ever discovered. Dr. Richard J. Howard, curator of fossil arthropods at the Natural History Museum and lead author on the study, says Praearcturus lived at least 50 million years earlier than other giant arthropods like Arthropleura, appearing well before trees existed, when life on land was only just getting started. According to Howard, confirming the animal as a scorpion changes what scientists understand about how and when these creatures evolved to such extraordinary sizes.

It may also have hunted in water, feeding on fish and other large aquatic animals. Its body structure, including triangular lateral extensions along the abdomen, points toward an aquatic or semi-aquatic lifestyle, consistent with the fossils turning up in ancient river sediments.

The largest scorpion alive today measures about 23 centimetres (9 inches). Praearcturus gigas was more than four times that length. Until this year, it was a crustacean.

Read the full story at Natural History Museum, June 3, 2026

Hot Take: "Giant woodlouse" was already an unacceptable animal. Somehow the correction made things worse.